Conveying rack cleaning in an electrodeposition process

ABSTRACT

A method for anti-corrosion coating of metal components, in series, comprising a plurality of wet-chemical treatment steps concluding in cathodic electrodeposition, in which method each component is received by a conveying rack; then the component and conveying rack proceed through all treatment steps; the finished coated component is separated from the conveying rack; and an uncoated component is then received by the same conveying rack for coating; wherein build-up of solid coating deposits on the conveying rack is prevented by using an additional treatment step before cleaning/degreasing, passivation and electrodeposition, thereby avoiding extraction of individual conveying elements for removing coating deposits; wherein removal of cathodic electrodeposition coating constituents from conveying racks is achieved by contacting the conveying racks carrying components to be coated with an aqueous acidic agent, containing phosphoric acid, before the wet-chemical treatment steps for cleaning/degreasing, passivation and cathodic electrodeposition.

The present invention relates to a method for anti-corrosion coating of metal components in series, the method comprising a plurality of wet-chemical treatment steps including cathodic electrodeposition, which completes the coating process, in which method each component is received by a conveying rack and then the transport pair consisting of the component and the conveying rack is guided through all the treatment steps, before the finished coated component is separated from the conveying rack and an uncoated component is received by the same conveying rack for coating, the build-up of solid coating deposits on the conveying racks being prevented in the method by the incorporation of an additional treatment step before degreasing/cleaning and the subsequent passivation and electrodeposition. In this way, the coating process from pretreatment to electrodeposition can be operated economically in a single system (“single loop”) in the method according to the invention, as the extraction of individual conveying elements for removing coating deposits does not take place after the pre-cleaning has been incorporated. In the context of the present invention, effective removal of the coating constituents received on the conveying racks from the cathodic electrodeposition is achieved simply by bringing the conveying racks, and thus also the components to be coated which are received by the conveying rack, into contact with an aqueous agent of suitable acidity containing phosphoric acid before the wet-chemical treatment steps for degreasing/cleaning, passivation and cathodic electrodeposition.

The anti-corrosion pretreatment of metal components, in particular consisting of the materials zinc, iron, steel, galvanized steel and/or aluminum, in a process sequence comprising passivation, for example based on water-soluble phosphates or based on water-soluble compounds of the elements Zr, Ti and/or Si, followed by electrodeposition, has been established or known in principle in the prior art for decades. In this case, the passivation can result in the formation of a crystalline conversion layer, for example a phosphate layer according to EP 2503025, or simply the formation of an amorphous coating, for example within the context of zirconium phosphating according to EP 2215285. The metal components passivated in this manner are usually transferred to the electrodeposition treatment step immediately after being rinsed. In order to transport the components through the previously outlined treatment steps of a conventional anti-corrosion coating process for metal surfaces of iron, zinc and aluminum materials, conveying racks are used in the automotive industry to hold the bodies and guide them through the treatment steps. Parts of the conveying racks are brought into contact with the bath solutions and rinsing solutions in the wet-chemical treatment steps. The coating is technically advantageous in an individual system in which a transport pair consisting of conveying racks together with the body is guided through all treatment steps, including the electrodeposition process, and the body is then separated from the conveying rack and discharged for the baking step, which involves drying, film-formation and curing of the electrodeposition system, and the conveying rack freed from the body receives an untreated and thus uncoated body in order to go through the coating process again (so-called “single-loop system”). Each conveying rack of such a single-loop system thus goes through all the wet-chemical treatment steps as often as is necessary to provide the specified series of bodies with anti-corrosion coating, or as often as possible before the system needs to be serviced. In systems of this kind, it is clear that the conveying racks have to be regularly cleaned of binder and pigment constituents adhering from the electrodeposition, which is a technically complex process as the electrodeposition constituents adhering to the conveying racks usually coagulate in the steps of cleaning/degreasing before the passivation step and cannot be removed simply by rinsing. Since each conveying rack repeatedly goes through the electrodeposition process for coating a large number of bodies, a coating coagulate having a considerable layer thickness builds up on the regions of the conveying rack that repeatedly come into contact with the electrocoating, which coagulate ultimately forms firmly adhering incrustations that can be removed mechanically from the conveying rack only with great effort. The latter is in particular the case with alkaline cleaning and degreasing if a cathodic electrodeposition is also provided for coating. Despite its fundamentally efficient operation, the economy efficiency of a single-loop system is therefore often not ensured, due to the required regular maintenance of the conveying racks and the associated system downtime compared to production lines in which the body is separated from its conveying rack after passivation and before electrodeposition and is received by a second conveying rack system for further coating. The object of the present invention is therefore to improve the economy of a single-loop system for anti-corrosion coating of metal components in series, comprising the cleaning/degreasing, passivation and cathodic electrodeposition thereof, by ensuring continuous operation of the coating system during series production.

This object is achieved in a method for anti-corrosion coating of metal components in series, the method comprising at least one cleaning/degreasing, passivation and cathodic electrodeposition as wet-chemical treatment steps in each case, the degreasing/cleaning step always preceding that of passivation in the process sequence for anti-corrosion coating and taking place on the basis of an aqueous cleaning solution, the pH value of which is above 6, and the treatment step of the cathodic electrodeposition always following that of passivation in the process sequence for anti-corrosion coating, in which method each component in the series to be pretreated is received by a conveying rack, and then the transport pair consisting of the component and the conveying rack is guided through the wet-chemical treatment steps according to the process sequence and the transport pair is separated only after the last treatment step and a component provided with anti-corrosion coating is extracted, and then the conveying rack which is released in this way receives a next component in the series in order to repeat the process sequence for the purpose of anti-corrosion coating of said component, the conveying rack going through the process sequence as often as is necessary to carry out anti-corrosion coating of the series of components, characterized in that at least the part of each conveying rack which is brought into contact with the dip coating in the cathodic electrodeposition is brought into contact with an aqueous agent in a pre-cleaning step after the final treatment step and a next component to be pretreated has been received, but before the treatment step of degreasing/cleaning, which aqueous agent has a total acid content of at least 3 points and contains phosphoric acid.

A metal component within the meaning of the present invention is present when the component is composed at least in part of at least one metal material, preferably zinc, iron, aluminum and the respective alloys, provided that the above-mentioned elements in each case form the main alloy constituent at more than 50 at. %, and of galvanized steel.

Anti-corrosion coating in series according to the present invention takes place if a plurality of metal components passes through the wet-chemical treatment steps, with the coating of each component being carried out one after the other and therefore at different times.

In the context of the present invention, a process sequence for anti-corrosion coating comprises a specified sequence of wet-chemical treatment steps from the structural component to be coated being received by the conveying rack to the now coated structural component being removed in order to be delivered to the subsequent treatment steps, e.g. the baking step, the structural component and at least parts of the conveying rack being brought into contact with an aqueous agent in each individual wet-chemical treatment step.

In the context of the present invention, a conveying rack is any device suitable for receiving, transporting and discharging the component, the suitability also consisting in being able to guide the component through the spatially separated wet-chemical treatment steps in accordance with the process sequence according to the invention and thereby both discharging as little material as possible into the treatment steps and receiving as little material as possible from the treatment steps. Conveying racks are therefore preferably made of materials that are inert with respect to the media applied in the treatment steps, for example stainless steel, and have an external design that minimizes retention of media from the treatment step in question into the following step. As soon as the component is received by the conveying rack, a transport pair is realized within the scope of the present invention, specifically until the component is transferred to a next system, in particular a conveying rack system, for further treatment outside the process sequence for anti-corrosion coating, for example for baking the electrodeposition, and is thus discharged. The conveying rack is released again as soon as the metal component provided with anti-corrosion coating according to the process sequence is extracted, and can receive another metal component to be provided with anti-corrosion coating. Generally, for reasons of economy of method, it is preferred to use a plurality of conveying racks for the quasi-continuous treatment of a plurality of components in series. Preferably, the number of conveying racks corresponds at least to the number of wet-chemical treatment steps.

In the context of the present invention, the total acid content in points is determined by diluting 10 ml of the aqueous agent of the pre-cleaning to 50 ml and titrating with 0.1 N sodium hydroxide solution to a pH of 8.5. The consumption of milliliters of sodium hydroxide solution indicates the point number of the total acidity. The pH corresponds to the negative decimal logarithm of the hydronium ion activity measured by means of pH-sensitive glass electrodes at 20° C. after calibration with pH buffer solutions suitable for the relevant pH range.

In the method according to the invention for anti-corrosion coating of metal components in series, each conveying rack is effectively freed from binder and pigment residues after the next component to be coated has again gone through all the treatment steps required for coating in the pre-cleaning. Separate maintenance of the conveying racks in order remove firmly adhering electrodeposition residues is therefore no longer necessary, such that said frames can repeatedly go through all wet-chemical treatment steps in a coating system and the advantages of operating with only one conveying rack system can thus be fully exploited. In the method according to the invention, the pre-cleaning is matched to the type of electrodeposition and requires an acidic aqueous agent for detaching cathodic dip coating residues from the conveying racks in the pre-cleaning.

In the context of the present invention, electrodeposition refers to a wet-chemical treatment step in the course of which a curable coating coagulate is deposited on the metal component under the application of an electrical voltage and is then formed into a film and cured by baking in a subsequent treatment step. For this purpose, the electrodeposition is preferably based on an aqueous agent containing at least one dispersed organic resin in an amount of at least 1 wt. % based on the aqueous agent. According to the invention, the electrocoating can be deposited cathophoretically, i.e. by applying an electrical voltage in which the metal component to be provided with anti-corrosion coating is connected as the cathode. Correspondingly, this is cathodic electrodeposition, in which an alkaline pH shift at the interface to the metal component causes coagulation of the dispersed resin particles, and thus layer formation on the component. Cathodic electrodeposition is established in particular for the anti-corrosion coating of passivated metal components, for example zinc-phosphated components or components coated with amorphous conversion layers, and is used as standard in coating automobile bodies. An epoxy resin is preferably used as a binder, which in turn is preferably selected from amine-modified polyepoxides, for the cathodic dip coating, the dip coating to be cathodically applied preferably also comprising blocked and/or unblocked organic compounds containing isocyanate groups as hardeners and particularly preferably also comprising at least one water-soluble compound of the element bismuth and/or of the element yttrium, each of which is able to exert a positive influence on the crosslinking of the coating coagulate in the baking step. In the context of the present invention, compounds of these elements are “water-soluble” when the solubility thereof in deionized water having a conductivity of no more than 1 μScm⁻¹ at a temperature of 20° C. is at least 1 g/kg.

The tendency of coating residues of cathodic dip coatings to coagulate in alkaline media results in the formation of solid coating deposits and incrustations on conveying racks which go through the process sequence for anti-corrosion coating of the series of metal components based on cathodic electrodeposition in single-loop operation, in particular if the conveying racks driven out of the dip coating process, after receiving the next component to be provided with anti-corrosion coating, first enter the treatment step of degreasing/cleaning, which is usually carried out on the basis of a neutral cleaner or an alkaline cleaner. Accordingly, it is essential to establish a method according to the invention for the economy of a single-loop system comprising a conventional process sequence consisting of degreasing/cleaning based on an aqueous cleaning solution having a pH above 6, passivation and cathodic electrodeposition, in which the cleaning/degreasing, as a wet-chemical treatment step within the process sequence for anti-corrosion coating of components in series, precedes the treatment step of passivation and in turn follows the treatment step of pre-cleaning. The aqueous cleaning solution for cleaning/degreasing is preferably alkaline and particularly preferably has a pH above 8, particularly preferably a pH above 10. The cleaning/degreasing based on the aqueous cleaning solution immediately follows the pre-cleaning, preferably without an intermediate rinsing step and without a drying step. In this context, “immediately” means without one or more intermediate wet-chemical treatment steps, which are not rinsing steps.

For effective detachment of dip coating residues from the conveying racks within a process sequence comprising cathodic electrodeposition, it is necessary according to the invention for the aqueous agent to have a total acid content of at least 3 points in the pre-cleaning.

In preferred embodiments, a higher acidity is preferred for providing agents for pre-cleaning with better cleaning performance for cathodic dip coating residues, such that the total acid content of the acidic aqueous agent of the pre-cleaning is preferably at least 5 points, particularly preferably at least 10 points and very particularly preferably at least 20 points. Accordingly, a pH of the aqueous agent in the pre-cleaning of less than 5.5 is preferred, particularly preferably a pH of less than 5.0 and particularly preferably a pH of less than 4.5. The rust formation on the metal components is largely suppressed in the presence of phosphoric acid, but it is preferred that the pH of the aqueous agent in the pre-cleaning is no less than 2.0, particularly preferably no less than 2.5. If a pH of the aqueous agent of less than 2.5 is required for the effective removal of dip coating residues on the conveying racks, it is therefore advantageous for the corrosion inhibitors known to a person skilled in the art to be added.

A certain buffer capacity has proven to be advantageous in the pre-cleaning in order to maintain a good separation performance with regard to the dip coating residues from the conveying racks, such that in methods using cathodic electrodeposition, preferably acids having a pKa value above 2.5, but below 5.5, are used to adjust the total acidity of the aqueous agent in the pre-cleaning. In a preferred embodiment, the proportion of acids having a pKa value in the preferred range of 2.5-5.5 contributes at least 80% to the total acid content. Suitable representatives of such acids are phosphoric acid, which is already obligatory, but also phosphoric acid esters, organic diphosphonic acids, α-hydroxycarboxylic acids and mono- and dicarboxylic acids, such as, for example, gluconic acid, acetic acid, citric acid or tartaric acid. Suitable acids, the pKa value of which is not above 2.5, and which can also be used to adjust the total acidity of the aqueous pre-cleaning agent, are nitric acid, sulfuric acid, ethylenediaminetetraacetic acid, etidronic acid and amidosulfonic acid.

In general, to ensure the performance of subsequent treatment steps due to the inevitable carry-over of active components from preceding treatment steps, it is advantageous if the type of acid used in the pre-cleaning or the salts thereof are also an active component of the subsequent wet-chemical treatment step. This is also technically advantageous for replenishing active components that have already been depleted in subsequent treatment steps. If, for example, in methods using cathodic electrodeposition, the passivation following the pre-cleaning is phosphating or if the pre-cleaning in such methods is followed by cleaning/degreasing containing phosphates as builder substances, the provision of the total acid according to the invention in the aqueous medium of the pre-cleaning based on the phosphoric acid already contained according to the invention is always advantageous, such that in a preferred embodiment the proportion of phosphoric acid in the acidic aqueous agent of the pre-cleaning is at least 60%, particularly preferably at least 80%, based on the total acid in points.

For the pre-cleaning in the method according to the invention based on an acidic aqueous agent containing phosphoric acid, it is preferred generally and for setting an optimal total acid content for the total phosphate content to be at least 3 g/kg, particularly preferably at least 5 g/kg, more particularly preferably at least 10 g/kg, very particularly preferably at least 20 g/kg, but preferably less than 50 g/kg, in each case calculated as PO₄ and based on the acidic aqueous agent of the pre-cleaning.

Adding surface-active compounds to the aqueous pre-cleaning agent may be beneficial for assisting the removal of electrocoating residues and is optional in the context of the present invention. Preferred surface-active substances are organic surfactants, particularly preferably non-ionic organic surfactants. Particularly suitable representatives of non-ionic organic surfactants having high compatibility with an alkaline degreasing/cleaning following the pre-cleaning are ethoxylated and/or propoxylated C8-C12, preferably C8-C10, fatty alcohols having a degree of ethoxylation of 5-11 and a degree of propoxylation of 1-7, each of which may be at least partially end-capped with C1-C4 monoalcohols.

Since, in the method according to the invention, the pre-cleaning of the transport pairs consisting of the conveying rack and the component to be coated serves only to separate the dip coating residues adhering to the conveying racks and thus to prevent the formation of incrustations thereon, there is generally no need for further additions to the aqueous agent used in the pre-cleaning, for example for the purpose of chemical conditioning of the surfaces of the components to be coated. In a preferred embodiment of the method according to the invention, the aqueous agent in the pre-cleaning therefore contains a total of less than 10 g/kg, particularly preferably less than 1 g/kg, of organic compounds and furthermore preferably less than 0.1 g/kg, particularly preferably less than 0.01 g/kg, of dispersed phosphates calculated as PO₄. Very particularly preferably, the aqueous agent in the pre-cleaning contains both a total of less than 0.1 g/kg, preferably less than 0.01 g/kg, of dispersed phosphates and a total of less than 10 g/kg, preferably less than 1 g/kg, of other dissolved compounds which, in the case of pre-cleaning in the method according to the invention, are not an acid having a pKa value above 2.5 and below 5.5.

The pre-cleaning of at least the part of each conveying rack which has been brought into contact with the cathodic electrodeposition, and preferably also of the component to be provided with anti-corrosion coating, is preferably carried out by immersion, flushing and/or spraying, the latter preferably with a spray pressure of at least 2 bar. The temperature of the acidic aqueous agent during the application in the pre-cleaning is preferably in the range of from 40 to 60° C. The contact time fluctuates depending on the application and the system, but is preferably between 5 and 60 seconds, particularly preferably between 10 and 30 seconds.

In a particular embodiment of the method according to the invention, bringing into contact with an aqueous wetting agent containing at least one water-soluble alcohol, preferably selected from 1,2-propanediol, ethylene glycol, glycerol, 1,4-butanediol and/or at least one water-soluble glycol ether, preferably a mono-alkyl ether having no more than 4 carbon atoms of di- or tripropylene(ethylene)glycol, is used for preparing good wetting of the conveying racks with the acidic aqueous agent and for better removal of the electrodeposition residues after the cathodic electrodeposition, at least the part of the conveying rack which is brought into contact with the acidic aqueous agent in the pre-cleaning being brought into contact with the aqueous wetting agent after the electrodeposition, but before the pre-cleaning, preferably also before the conveying rack receives the component to be provided with anti-corrosion coating. In this context, an alcohol or glycol ether is water-soluble within the meaning of the present invention if at least 10 g of the alcohol or the glycol ether can be dissolved in the homogeneous phase in one kilogram of deionized water having a conductivity of no more than 1 μScm⁻¹ at a temperature of 20° C. Bringing into contact with the aqueous wetting agent takes place preferably for at least 5 seconds, particularly preferably for at least 10 seconds, but preferably no longer than 60 seconds.

In the context of the present invention, passivation refers to at least one wet-chemical treatment step, in the course of which a substantially inorganic coating is produced on at least one surface of a metal material of the component to be provided with anti-corrosion coating in a coating layer of at least 10 mg/m². Passivation is substantially inorganic if the area-related ratio of TOC content to layer coating in each case is less than 0.2 in milligrams per square meter, the TOC content being determined differentially gravimetrically after pyrolysis of a dried passivation in a nitrogen atmosphere at a peak metal temperature of 600° C. In particular embodiments, the passivation is carried out on the basis of acidic aqueous treatment solutions which contain dissolved phosphates and/or water-soluble compounds of the elements Zr, Ti and/or Si, very particularly preferably on the basis of phosphating, in particular zinc phosphating, which is usually applied by means of acidic aqueous solutions containing 0.3-3 g/kg of zinc ions and 5-50 g/kg of phosphate ions and preferably provides layer weights in the range of 0.5-4 g/m² calculated as PO₄. Zinc phosphating usually comprises several wet-chemical treatment steps, since it is regularly necessary to activate the metal surfaces before the actual zinc phosphating, i.e. the formation of a conversion layer, which is preferably carried out using alkaline, adjusted dispersions containing phosphate particles. In particular for passivations based on dissolved phosphates, the method according to the invention ensures that an additional carry-over of phosphate ions from the passivation into the electrodeposition is prevented by coating adhering to the conveying racks, such that there is no risk of the dip coating being destabilized by increased phosphate entry in methods according to the invention. The absorption of dissolved phosphate by coating residues on the conveying racks from the passivation treatment step and the carry-over thereof into the electrodeposition is particularly promoted in methods using cathodic electrodeposition, which may be related to the positive zeta potential of the resin particles or the positive charge density in the polymer of the binder of cathodic dip coatings. In a particularly preferred embodiment, the method according to the invention therefore relates to the anti-corrosion coating of metal components in series, the method comprising at least degreasing/cleaning, zinc phosphating and cathodic electrodeposition as wet-chemical treatment steps in each case, the degreasing/cleaning step always preceding that of zinc phosphating in the process sequence for anti-corrosion coating and taking place on the basis of an aqueous cleaning solution, the pH value of which is above 6, and the treatment step of the cathodic electrodeposition always following that of zinc phosphating in the process sequence for anti-corrosion coating, in which method each component in the series to be pretreated is received by a conveying rack, and then the transport pair consisting of the component and the conveying rack is guided through the wet-chemical treatment steps according to the process sequence and the transport pair is separated only after the last treatment step and a component provided with anti-corrosion coating is extracted, and then the conveying rack which is released in this way receives a next component in the series in order to repeat the process sequence for the purpose of anti-corrosion coating of said component, the conveying rack going through the process sequence as often as is necessary to carry out anti-corrosion coating of the series of components, at least the part of each conveying rack which is brought into contact with the dip coating in the cathodic electrodeposition being brought into contact with an aqueous agent in a pre-cleaning step after the final treatment step and a next component to be pretreated has been received, but before the treatment step of zinc phosphating, which aqueous agent has a total acid content of at least 3 points and phosphoric acid and preferably a pH of no less than 2.5.

In general, it is preferred in the method according to the invention that the treatment step following the pre-cleaning and the passivation in each case follows these steps immediately, i.e. with or without an intermediate rinsing step, but without a drying step. In this context, “immediately” means without one or more intermediate wet-chemical treatment steps, which are not rinsing steps. If reference is made to carrying out a “rinsing step” in the context of the present invention, this is always a process which is solely intended to remove a wet film adhering to the component from an immediately preceding wet-chemical treatment step from the surface of the component and in this way to prevent components from wet-chemical treatment steps from being carried over into subsequent steps. In the context of the present invention, a “drying step” denotes, in contrast, a process in which the surfaces of the metal component that have a wet film are intended to be dried with the aid of technical measures, for example by supplying thermal energy or passing a stream of air thereover.

Moreover, it is conventional, and therefore preferred, for the baking of the dip coating in order to form a cured coating to follow on from the process sequence for anti-corrosion pretreatment of components in series in the method according to the invention, with conveying racks, which are not conveying racks of the kind associated with the process sequence for anti-corrosion pretreatment, preferably in turn receiving the pretreated components and transferring said components to the baking step and optionally subsequent steps for further coating. 

1. A method for anti-corrosion coating of metal components in series, the method comprising at least one cleaning/degreasing step, a passivation step and a cathodic electrodeposition step, as wet-chemical treatment steps in each case, in a process sequence for the anti-corrosion coating of the metal components, the cleaning/degreasing preceding the passivation and taking place by contact with an aqueous cleaning solution having a pH value of above 6, and the treatment step of the cathodic electrodeposition following that of the passivation and taking place by contact with a dip coating; wherein each component in the series to be pretreated is received by a conveying rack, then a transport pair comprising the component and the conveying rack is moved through the wet-chemical treatment steps according to the process sequence, the transport pair is separated only after a last treatment step in the process sequence for anti-corrosion coating and a component provided with anti-corrosion coating is extracted thereby releasing the conveying rack which then receives a next component in the series in order to repeat the process sequence for the anti-corrosion coating of said next component, the conveying rack going through the process sequence as often as is necessary to carry out anti-corrosion coating of the series of components; wherein at least a part of each conveying rack, that is brought into contact with the dip coating in the cathodic electrodeposition, is contacted with an aqueous pre-cleaning agent in a pre-cleaning step taking place after said last treatment step and after the next component to be pretreated has been received, but before the treatment step of cleaning/degreasing, wherein the aqueous pre-cleaning agent has a total acid content of at least 3 points and contains phosphoric acid.
 2. The method according to claim 1, wherein the dip coating in the cathodic electrodeposition is based on an epoxy resin as a binder, and the epoxy resin is selected from amine-modified polyepoxides.
 3. The method according to claim 2, wherein the aqueous pre-cleaning agent has a pH of less than 5.5 and does not fall below 2.5.
 4. The method according to claim 3, wherein the aqueous pre-cleaning agent has a pH of less than 5 and the total acid content thereof is at least 10 points; and the dip coating comprises blocked and/or unblocked organic compounds containing isocyanate groups as hardeners and further comprises at least one water-soluble compound of the element bismuth and/or of the element yttrium.
 5. The method according to claim 1, wherein the aqueous pre-cleaning agent has a total phosphate content of at least 3 g/kg and less than 50 g/kg of the aqueous pre-cleaning agent, the phosphate in each case calculated as PO₄.
 6. The method according to claim 5, wherein the total phosphate content is at least 10 g/kg of the aqueous pre-cleaning agent; and said pre-cleaning agent further comprises one or more surfactants.
 7. The method according to claim 6, wherein the aqueous pre-cleaning agent further comprises one or more non-ionic surfactants.
 8. The method according to claim 7, wherein the one or more non-ionic surfactants are selected from ethoxylated and/or propoxylated C8-C12 fatty alcohols having a degree of ethoxylation of 5-11 and degree of propoxylation of 1-7.
 9. The method according to claim 1, wherein at least the part of each conveying rack which has been brought into contact with the cathodic electrodeposition, and optionally also the component to be provided with anti-corrosion coating which is received by the conveying rack, is brought into contact with the aqueous pre-cleaning agent in the pre-cleaning step by immersion, flushing and/or spraying.
 10. The method according to claim 1, wherein bringing into contact with the aqueous pre-cleaning agent in the pre-cleaning step takes place at a temperature in a range of from 40 to 60° C.
 11. The method according to claim 1, further comprising contacting the part of the conveying rack, which is brought into contact with the dip coating in the cathodic electrodeposition, with an aqueous wetting agent after the cathodic electrodeposition step, but before the pre-cleaning step, and optionally also before the conveying rack receives the component to be provided with anti-corrosion coating, wherein the aqueous wetting agent comprises at least one water-soluble alcohol and/or at least one water-soluble glycol ether.
 12. The method according to claim 11, wherein the at least one water-soluble alcohol is selected from 1,2-propanediol; ethylene glycol; glycerol; 1,4-butanediol and combinations thereof; and contact with the wetting agent takes place for at least 5 seconds and no longer than 60 seconds.
 13. The method according to claim 1, wherein the treatment step following the pre-cleaning and the passivation in each case follows these steps immediately, with or without an intermediate rinsing step, but without a drying step.
 14. The method according to claim 1, wherein the treatment step of cleaning/degreasing immediately follows that of pre-cleaning without an intermediate rinsing step and without a drying step.
 15. The method according to claim 1, wherein the passivation step is carried out by contact an acidic aqueous zinc phosphating treatment solution.
 16. The method according to claim 1, wherein the treatment step of cleaning/degreasing is carried out on the basis of an alkaline aqueous cleaning solution having a pH above
 8. 17. The method according to claim 1, wherein baking of the dip coating applied in the cathodic electrodeposition step, in order to form a hardened paint coating, follows the process sequence for the anti-corrosion coating of components in series using conveying racks, which are not conveying racks associated with the process sequence for anti-corrosion coating. 